Why do we have fingerprints or 'prints' on only
our palms and feet? Is there a difference between
the types of the skin?

Question Date: 2011-10-28

Answer 1:

Good observation! The skin on our hands and
feet is different. First, we dont have any hair
there. Even places on your body that dont seem to
have hair usually have short, fine hair. But the
soles and palms have none. There are a lot of
sweat glands here too.

For another thing,
theres less pigment (color). Even people with
very dark skin elsewhere usually have
pinkish-white palms of their hands and soles of
their feet.

The skin is also thicker (about
8-14 times thicker) here, which makes sense since
theres so much chance to wear down these areas.
The cells here divide sooner, while they are still
smaller than skin cells in other places. The
differences in color and thickness are because of
one gene that makes a protein called DKK1. The
body only makes this protein on the palms and
soles.

Fingerprints (and footprints) are
tiny ridges in the surface part of the skin
(epidermis) that are formed by lines in the deep
skin (dermis). They probably give us better grip
by giving our skin more friction. They may also
help keep the skin from tearing easily.

Scientists still havent figured out why the
patterns are so different, but it probably has to
do with ridges that form when the skin is first
formed, only about 2 months after an egg is
fertilized. As the growing layers push and pull,
permanent ridges are made. We are born with the
same fingerprints that we will have all of our
lives.

Do you think identical twins have
identical fingerprints?

Thanks for asking,

Answer 2:

The leading theory as to why we have
fingerprints is that it enhances our sense of
touch. The ridges are thought to pick up
vibrations as we run our fingers (or toes) over a
surface, giving our brains more physical input
about whatever it is that we are touching. It
makes sense, then, that we have evolved to only
have fingerprints on our palms and bottom of our
feet, since that is what we use by and large to
explore our physical environment. This is also why
we have a much higher level of sensory molecules
and nerves in our hands and feet than in other
places in our skin. You can test this by taking
something with a really fine point, like a pen or
a needle, and gently touching your fingertip and
then the top of your forearm. You can have a
friend do it while you close your eyes and see if
you can tell when they touch your arm.

Here
is a short article on fingerprints and how they
enhance our sense of touch:

Let me begin by saying that the skin on the
palms of your hands and feet is different, which
is why palms have "finger" prints. To the best of
my knowledge, people aren't sure why the skin
there is different, but there was an article in a
respected science journal (think of a blog where
scientists promote and publish their ideas) a
couple years ago, that suggested fingerprints
helped improve our ability to feel texture. That
is, they make our sense of touch more
sensitive.

On an interesting note, no one
really knows why your fingers prune up when they
get wet! It's actually a reflex! It's not that
they just soak up water and buckle, like many
people incorrectly believe. A recent scientific
article in a respected science journal put forward
the idea that the skin on your hands and feet
prunes up and leads to better grip, particularly
when wet. Although it's debated, this group
suggested that the pruning skin acted like treads
on a tire, and helped remove water while retaining
better grip. However, it's just a hypothesis, and
many people disagree.

Answer 4:

Fingerprints are a result of distinct ridges on
the skin that do not change over time and are
unique to each person. Even identical twins do
not have the same fingerprints. Our fingerprints
develop while we are still in the womb and may
have evolved so we could grip things better. This
may explain why prints are only on surfaces we use
to grip items with, our fingers (and our
evolutionary ancestors used their toes for
gripping as well).

The fingerprints are
produced from a layer in the skin called the
papillary layer, which is a layer within the
dermis layer of skin. It produces an extra thick
layer to form the ridges of fingerprints. The
papillary layer is found in all skin but only
produces extra thick parts on the hand and feet
and as a result those are the only areas with
"prints."